Along with the recent rapidly increasing demand for portable electronic products, such as notebook computers, video cameras and mobile phones, and the accelerated development of energy storage batteries, robots, satellites, etc., considerable research has been conducted on high-performance secondary batteries capable of repeated charging/discharging.
Currently commercially available secondary batteries include nickel-cadmium batteries, nickel-metal hydride batteries, nickel-zinc batteries and lithium secondary batteries. Lithium secondary batteries can be charged and discharged freely because there is little to no memory effect and have very low self-discharge rate and high energy density. Due to these advantages, lithium secondary batteries have received a great deal of attention compared to nickel-based secondary batteries.
On the other hand, carbon energy resources have gradually depleted and interest in environmental issues has steadily risen. Under such circumstances, demand for hybrid and electric vehicles has been continuously increasing worldwide, including the United States, Europe, Japan and Korea. Since hybrid and electric vehicles receive driving force from the charge/discharge energy of the battery packs, they have high fuel efficiency and release reduced amounts or no amount of pollutants into the environment in comparison with engine driven vehicles. From the viewpoint of economic efficiency and environmental protection, hybrid and electric vehicles have received a positive consumer response. Thus, more attention and research have been concentrated on vehicle batteries as key components of hybrid vehicles and electric vehicles.
Hybrid and electric vehicle batteries use their discharge energy. For this inherent reason, hybrid and electric vehicle batteries may be fully discharged. To protect a battery of a general electric or hybrid vehicle from being fully discharged, the charging state of the battery is displayed on a gauge on a driver's seat to inform the driver of the remaining charge amount. In addition, an alarm system is mounted such that when the remaining charge amount of a battery is at a predetermined level or below, a warning lamp is lit or a warning sound is generated to inform a driver that his/her vehicle needs charging. However, a vehicle battery may be fully discharged in many cases, for example, when a driver travels through an area where there is no electric charging station, fails to find an electric charging station during travelling, or does not recognize or forget to watch the warning lamp indicating a full discharge of the battery and continues to travel. A full discharge of a vehicle battery may also take place after the vehicle has been left unused for a long time in a state in which the remaining charge amount of the vehicle battery is low.
Generally, there are no serious problems that come with a fully discharged battery since one can just stop using the portable product for some time. Unlike other portable products, however, a fully discharged battery of an electric or hybrid vehicle requires immediate charging. Particularly, since an electric vehicle is only driven by a battery, it is impossible to use upon full discharge. Accordingly, in situations where a battery of a vehicle a driver must use is fully discharged or in a case where the battery is fully discharged while travelling outside his/her residence, immediate charging of the vehicle battery is required.
In such a situation, unless at a place where the vehicle battery can be charged, the driver must call a tow truck and ask to tow the vehicle to a place where the battery can be charged. However, additional costs must be paid, the longer the time it takes to tow the vehicle. In addition, when a vehicle is being towed, there is an inconvenience for the driver and/or passengers having to uncomfortably ride the tow truck and if the number of passengers exceeds the number of available seats on the tow truck, the passengers will either have to ride the vehicle being towed or find some other form of transportation. Not only is this cumbersome but also increases the risks of an accident, which could also lead to fatally threatening the lives of many people.